1. Field of the Invention
The present invention relates to location and monitoring systems, and more particularly, to systems using micropower transponders for locating and monitoring individuals, animals, or objects.
2. Description of the Related Art
A victim of abduction is usually unable to communicate his or her location or details of the abduction. For example, the victim may be restrained, or otherwise disabled. Often the victim will be gagged, and thus unable to speak. If the victim is able to escape and elude the captors, the victim may be confused and lack identification documents. Further, a kidnapped child may lack the verbal skills to provide sufficient information for rescue. A victim of abduction, who is unable to communicate or who is deprived of opportunities to obtain assistance, is especially vulnerable. Valuable animals or objects are also frequently lost or stolen and are difficult to locate.
In principle, individuals at high risk of abduction could carry a cellular telephone or a device that utilizes the global positioning system and a transmitter, or some other locating or direction finding system. Unfortunately, any conspicuous device carried by a victim can be easily removed and quickly disposed of by the captors. Further, the implementation of a terrestrial-based locating or direction finding system over the entire surface of the Earth requires the installation of a very expensive infrastructure. Coverage over very large geographic areas is not economical with terrestrial systems. In addition, global positioning receivers and other types of locating and direction finding systems have poor performance in built-up urban areas.
The long history of satellite Doppler tracking for position determination has proven that a constellation of low Earth-orbiting satellites can be used to track people, animals, or objects on the surface of the Earth. In 1957, the British developed satellite Doppler tracking to determine the orbit of the first artificial satellite. Broadcasts from Sputnik were monitored, and the Doppler shifts due to the relative motion of the satellite to ground-based receivers were measured. The changes in the Doppler shifts were then used to calculate the position vector between Sputnik and the ground receivers. In 1963, the U.S. Navy Transit system became operational. Broadcasts from Transit satellites were used to locate Navy ships equipped with Transit receivers to an accuracy of a few hundred meters. Multiple observations of Transit signals were later used for ground surveys to sub-meter accuracy. In recent years, satellite Doppler tracking has also been used in the international search and rescue satellite (SARSAT) system to locate distress signals from SARSAT beacons.
Technical advances in small satellite design and construction in recent years have created the opportunity to provide inexpensive satellite-based telephone and pager services to individuals. For example, Iridium Inc.'s planned constellation of 66 satellites is expected to begin voice messaging commercial service by the end of 1998 or early 1999. Satellites for systems that will compete with Iridium are also under construction by Loral and various industry consortiums.
Animal tracking tags using Ultra High Frequency (UHF) Transmitters provide long-range tracking through orbiting satellite receivers by using very low data rates. The low data rates allow the use of very narrow bandwidths to communicate the animal's identification and to determine the animal's position by measuring the Doppler shift of the transmitter's carrier. This technique was first demonstrated using the OSCAR 6 amateur radio satellite and has been used to locate Emergency Locator Transmitters (ELT) from downed aircraft and hikers. Unfortunately, narrow band systems can only service a limited number of tags.
Conventional medical monitoring devices that monitor patient vital signs generally operate only within institutional settings such as in a hospital, school, or prison facility. Therefore, these medical monitoring devices are not designed for wide-area or global service areas. Furthermore, the medical devices are not adapted for use in a global location and monitoring system.
Child monitoring devices that use two portable units, one for the child and one for the parent, are applicable only to very special situations and are intended to operate in a very limited geographical area. Ground-based location systems, such as LORAN C, LoJack, Teletrac, and the like, all have limited geographic coverage, usually confined to large metropolitan or coastal areas.
To summarize, existing systems do not provide for global location of missing persons, animals, or lost objects using an implantable or hidden transponder, for collecting, transmitting and analyzing data over predetermined periods of time. Furthermore, existing systems do not provide remotely accessible archives of data, as opposed to summary data, in which data is accumulated over a period of time.